This invention relates to a mechanical disc brake of the type in which a brake lever rotates in response to a rotational input which is imparted thereto by a cable and the like and the rotational input imparted to the lever is then converted into a linear output which in turn effects a braking action and more particularly, to a mechanical disc brake which has a manual clearance adjusting means adapted to provide a predetermined or desired braking force by adjusting the clearances between the brake disc and friction pads so as to maintain the clearances within a predetermined value range at all times.
There have been proposed and practically employed a variety of brake discs having a mechanism adapted to convert a rotational input into a linear output and in any of the conventional disc brakes of the type, an axially movable push rod is adapted to directly receive an input to apply friction pads against a disc and a nut member is disposed on the push rod to rotate about the push rod and also to move linearly together with the push rod in the axial direction of the rod under the action of steel balls which displace along spherical faces. The nut member is fitted in and supported by a housing or a stationary member secured to the housing. That is, the entire nut member is fitted in and supported by the housing or the stationary member secured to the housing, in threaded engagement with the push rod and held in position by steel ball holding faces.
Such arrangement of the nut member in the conventional disc brake has the disadvantages that smooth rotation of the nut member is precluded due to varying tolerances in the manufacture of component parts and more particularly, due to the deviation of the center of rotation of the nut member support face from the center of rotation of the steel balls and in other words, due to the variation of the center of rotation determined by a plurality of steel balls (in most cases, three steel balls) from the center of rotation determined by the nut member supporting face and that the nut supporting portion of the housing or the stationary support member is easily subjected to wear. Furthermore, since a clearance is present in the nut supporting portion for rotatably receiving the nut member, the nut supporting portion wears away prematurely due to vibration of the brake device.
In the manual brake clearance adjusting means referred to hereinabove, the push rod adapted to transmit the linear movement produced by the mechanism which is designed to convert the rotational movement into the linear movement to the friction pad is provided with threads and the push rod is turned at one end by a screw driver or the like tool whereby the push rod is screwed out of the nut member which is in threaded engagement with the push rod so as to adjust the brake clearance. The other end of the push rod is formed with a polygonal cross-section configuration such as square or hexagonal configuration and a rotation regulation member engages the polygonal cross section end to prevent inadvertent rotation of the push rod which may occur due to vibration or other undesirable movement of the push rod so as to effect correct clearance adjustment.
In one example of the above-mentioned type of brake discs, the rotation regulation member is secured to one friction pad in consideration of the limited space within the disc brake as shown in commonly owned co-pending U.S. patent application Ser. No. 657,623, filed Feb. 12, 1976, now U.S. Pat. No. 4,022,299. In such arrangement, great difficulty is encountered in mounting a dust cover which is adapted to protect the rotation regulation member from moisture, mud and dust and as a result, the dust cover can not be employed in that earlier type of disc brake. Therefore, the disc brake has the disadvantage that mud, dust and other foreign matter tends to adhere to the rotation regulation member to the extent that the rotation regulation member comes to a standstill and rusts prematurely to thereby render the clearance adjustment operation difficult.
Furthermore, the component parts of such earlier disc brake are required to be fabricated and processed with high precision so that the polygonal cross-section end of the push rod can properly engage the rotation regulation member.
And in the brake device of the type referred to hereinabove, when the friction pad or pads are desired to be replaced by a new friction pad or pads, since it is very difficult to confirm whether the rotation regulation member is in proper engagement with a suitable position on the push rod, such confirmation is often neglected and as a result, the rotation regulation member is easily damaged.